Waveguide couplers

ABSTRACT

A coupler consists of two lengths of waveguide having a common narrow wall and which are capable of supporting the TE10 and TE20 modes of wave propagation, and inserted in a gap in said wall substituting for the part removed from the gap, a reactive structure having elements resonant at a predetermined operating frequency and situated in succession along the guide. The coupler can be used as a simple coupler when the elements are constituted by three closed rings and couple energy fed in at the input of one guide into the other guide or as a diplexer when there are six rings and energies at two different frequencies are fed to the input ends of the guides.

ilite ttes ate] [72] Inventor Roderick Edward Newbould Chelmsford,England [21] Appl. No. 43,851 [22] Filed June 5, 1970 [45] Patented Oct.19, 1971 [73] Assignee The Marconi Company Limited London, England [32]Priority June 13, 1969 [33] Great Britain [31] 30,037/69 [54] WAVEGUIDECOUPLERS 15 Claims, 4 Drawing Figs.

[52] US. Cl 333/10, 333/73 W, 333/82 R, 333/98 R [51] Int. Cl H01p 5/14,H03h 7/02, H03h 7/04 [50] Field of Search 333/10,1, 6,11, 73, 73 W, 98,98 M, 82

[56] References Cited UNITED STATES PATENTS 2,566,386 9/1951 Varian333/73 X Primary Examiner-Herman Karl Saalbach Assistant Examiner-MarvinNussbaum Att0rneyBaldwin, Wight, Diller & Brown ABSTRACT: A couplerconsists of two lengths of waveguide having a common narrow wall andwhich are capable of supporting the TB and T15 modes of wavepropagation, and inserted in a gap in said wall substituting for thepart removed from the gap, a reactive structure having elements resonantat a predetermined operating frequency and situated in succession alongthe guide. The coupler can be used as a simple coupler when the elementsare constituted by three closed rings and couple energy fed in at theinput of one guide into the other guide or as a diplexer when there aresix rings and energies at two different frequencies are fed to the inputends of the guides.

PATENTEDIICI I9 Ian 7 3,61 4,672

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ATTORNEYS PATENTEDUBI 19 Ian 3,614,672

' sum 20F 2 f? f INVENTOR BY 'aiwuo W 1 a Mo ATTORNEYS WAVEGUIDECOUPLERS This invention relates to waveguide couplers and has for itsmain object to provide improved frequency selective waveguide couplers.Though not limited to its application thereto, the invention isparticularly advantageous when applied to waveguide diplexers in whichapplication it enables diplexers to be made of considerably smallerdimensions and lower insertion losses than comparable known waveguidediplexers.

According to this invention a waveguide coupler comprises two lengths ofrectangular waveguide having a common narrow wall and capable ofsupporting the TE and TE modes of wave propagation and, inserted in agap in said common wall so as to substitute for the part thereof removedto form said gap, a reactive structure having at least three reactiveelements resonant at or near a predetennined operating frequency andsituated in succession in the direction of length of the guide.

In the case of a simple coupler the reactive elements couple energy fedin at the input end of one guide into the other guide. Such a couplercan, however, be used as a diplexer by feeding in energies at twodifferent frequencies to the input ends of the two guides. By making thereactive elements resonant at or near one of these frequencies theresult is achieved that the input of that frequency fed in to one guideis coupled into the other guide whereas the input, fed into the otherguide, and of the other frequency, remains in and passes virtuallyunchanged along the guide into which it was fed.

Preferably the reactive elements are in the form of closed ringssituated one behind the other at quarter wavelength intervals along thecenterline of the common wall, these rings being held in position bysupporting links joining them one to another and to the said common wallat opposite ends of the gap therein, said links being situatedsubstantially at positions of zero electrical field so as to be, fromthe electrical point of view, of no effect. The word rings is here usedin a wide sense to include not only rings of circular shape but rings ofother shapes, e.g., rectangular. Rings of rectangular shape arepreferably locally thickened on the opposite horizontal members toreduce the possibility of voltage breakdown.

Preferably a simple coupler has only three rings.

Preferably a coupler being used as a diplexer has six rings. These maybe connected in a single group. However for reasons of constructionalstrength and rigidity the rings are connected in two groups each havingthree rings.

In order to suppress unwanted modes of wave propagation the input andoutput ends of the guides are preferably stepped.

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a diagrammatic view partly in section of a coupler being usedas a diplexer in accordance with this invention,

FIG. 2 is a simplified energy transfer diagram used for the purpose ofexplanation of the arrangement of FIG. 1, and

FIGS. 3 and 4 are explanatory mode theory diagrams also used inconnection with the arrangement of FIG. 1.

Referring to FIG. I the frequency selective coupler is arranged for useas a diplexer and consists of two lengths of rectangular waveguide l and2 capable of supporting the TB and TE modes. The guides l and 2 haveinput ports 3 and 4 and output ports 5 and 6 respectively and a commonnarrow wall 7. In the plane of the wall 7 and arranged in holes thereinis a reactive structure of closed rings 8. There are six rings arrangedin two groups of three, each ring in a group being spaced at quarterwavelength intervals along the common wall. The rings are held inposition by supporting limbs 9 joining them one to another and to thecommon wall 7 both at the extreme ends of the groups and between thegroups at the 3 db. point 10. The links are situated at positions ofzero electric field.

An understanding of the operation of the diplexer of FIG. 1 will beassisted by reference to FIG. 2.

Input signals fl and 12 which can be in practice signals of frequency1,260 MHz. and 1,350 MHz. respectively are applied to input ports 3 and4 of guides l and 2 respectively.

These frequencies are given by way of example and other suitablefrequencies-could be used. The reactive rings 8 are made resonant at ornear frequency f2 so that input 12 fed in into guide 2 remains in andpasses virtually unchanged along that guide whereas the input fl fedinto guide I is coupled into guide 2. Half of signal fl is coupledthrough structure 8 before the 3 db. point 10 and the remainder after.It can be seen that both signals fl and 12 are taken off at port 6.

This coupling effect is achieved by coupling to the TE and TE modes inthe double width waveguide. The TE, mode has a phase velocity less thanthat of the TE, mode and by placing the reactance in the common narrowwall of the waveguides, the TB mode phase velocity is further decreased.This increases the relative phase changes of the two modes as theytravel along the waveguide. This change may best be seen from FIGS. 3and 4 of the drawings which show diagrammatically the relative phasechanges which occur for the TE and TE, modes in guides 1 and 2 for inputsignals f1 and f2 respectively. These changes have been drawn inseparate diplexers for simplicity. However, it should be appreciatedthat in practice they occur in the same coupler. The TE mode waves arerepresented by broken dashed lines, the TE mode by chain lines and theresultant mode by solid lines.

As can be seen from FIG. 3 the input ends 3 and 4 and output ends 5 and6 of the guides 1 and 2 are provided with stepped portions to suppressthe undesirable TE mode. This stepping was not shown in FIGS. 1 and 2for ease of drawing.

It should be noted that the horizontal members of the rectangular rings8 may be locally thickened to reduce the possibility of voltagebreakdown.

Couplers in accordance with the present invention have the advantagethat using rectangular loops of dimensions of the order of 3X2 withla-spacing links they can be made just 1 Meet long as opposed tocomparable known devices which are approximately 14 feet long. Similarlydiplexers in accordance with this invention can be made 3 feet long asopposed to comparable known diplexers which are approximately 25 feetlong. The above dimensions are given by way of example and are notintended to be limiting.

Iclaim:

l. A waveguide coupler comprising two lengths of rectangular waveguidehaving a common narrow wall and capable of supporting the TE and TEmodes of wave propagation; means defining a gap formed in said commonwall; a reactive structure inserted in said gap so as to substitute forthe part of the common wall removed to form said gap, said reactivestructure having at least three reactive elements in the form of closedrings resonant at or near a predetermined operating frequency andsituated one behind the other at quarter wavelength intervals along thecenterline of the common wall; and supporting links joining the ringsone to another and to the said common wall at opposite ends of the gaptherein, said links being situated substantially at positions of zeroelectrical field (when the coupler is in operation) so as to be, fromthe electrical point of view, of no effect.

2. A waveguide coupler as claimed in claim 1 wherein the rings are ofrectangular shape and are locally thickened on the opposite horizontalmembers for reducing the possibility of voltage breakdown.

3. A waveguide coupler as claimed in claim 1 wherein said rings consistof three rings.

4. A waveguide coupler as claimed in claim 2 wherein said rings consistof three rings.

5. A waveguide coupler as claimed in claim 1 wherein said rings consistof six rings connected in two groups of three rings whereby the couplermay be used as a diplexer.

6. A waveguide coupler as claimed in claim 2 wherein said rings consistof six rings connected in two groups of three rings whereby the couplermay be used as a diplexer.

'7. A coupler as claimed in claim 1 wherein input and output ends of thelengths of waveguide are stepped.

8. A coupler as claimed in claim 2 wherein input and output ends of thelengths of waveguide are stepped.

9. A coupler as claimed in claim 3 wherein input and output ends of thelengths of waveguide are stepped.

10. A coupler as claimed in claim 4 wherein input and output ends of thecoupler are stepped.

11. A coupler as claimed in claim 4 wherein input and output ends of thelengths of waveguide are stepped.

12. A coupler as claimed in claim 5 wherein input and output ends of thelengths of waveguide are stepped.

13. A coupler as claimed in claim 6 wherein input and output ends of thelengths of waveguide are stepped.

14. A waveguide coupler as claimed in claim 1 wherein energies at twodifferent frequencies are fed to input ends of

1. A waveguide coupler comprising two lengths of rectangular waveguidehaving a common narrow wall and capable of supporting the TE10 and TE20modes of wave propagation; means defining a gap formed in said commonwall; a reactive structure inserted in said gap so as to substitute forthe part of the common wall removed to form said gap, said reactivestructure having at least three reactive elements in the form of closedrings resonant at or near a predetermined operating frequency andsituated one behind the other at quarter wavelength intervals along thecenterline of the common wall; and supporting links joining the ringsone to another and to the said common wall at opposite ends of the gaptherein, said links being situated substantially at positions of zeroelectrical field (when the coupler is in operation) so as to be, fromthe electrical point of view, of no effect.
 2. A waveguide coupler asclaimed in claim 1 wherein the rings are of rectangular shape and arelocally thickened on the opposite horizontal members for reducing thepossibility of voltage breakdown.
 3. A waveguide coupler as claimed inclaim 1 wherein said rings consist of three rings.
 4. A waveguidecoupler as claimed in claim 2 wherein said rings consist of three rings.5. A waveguide coupler as claimed in claim 1 wherein said rings consistof six rings connected in two groups of three rings whereby the couplermay be used as a diplexer.
 6. A waveguide coupler as claimed in claim 2wherein said rings consist of six rings connected in two groups of threerings whereby the coupler may be used as a diplexer.
 7. A coupler asclaimed in claim 1 wherein input and output ends of the lengths ofwaveguide are stepped.
 8. A coupler as claimed in claim 2 wherein inputand output ends of the lengths of waveguide are stepped.
 9. A coupler asclaimed in claim 3 wherein input and output ends of the lengths ofwaveguide are stepped.
 10. A coupler as claimed in claim 4 wherein inputand output ends of the coupler are stepped.
 11. A coupler as claimed inclaim 4 wherein input and output ends of the lengths of waveguide arestepped.
 12. A coupler as claimed in claim 5 wherein input and outputends of the lengths of waveguide are stepped.
 13. A coupler as claimedin claim 6 wherein input and output ends of the lengths of waveguide arestepped.
 14. A waveguide coupler as claimed in claim 1 wherein energiesat two different frequencies are fed to input ends of the lengths ofwaveguide whereby the coupler may be used as a diplexer.
 15. A waveguidecoupler as claimed in claim 14 wherein the reactive elements areresonant at or near one of the said frequencies whereby the result isachieved that the input of that frequency fed into one of said lengthsof waveguide is coupled into the other of said lengths of waveguide, andthe input of the other of said frequencies remains in and passesvirtually unchanged along length of waveguide into which it was fed.